Deciding whether IR35 applies involves the underlying nature of a worker’s
relationship with a client being considered, in particular to examine
whether the worker would in law have been an employee if they had not been
engaged by the client via the PSC, in other words, whether the worker would
have been an employee if they had contracted directly with the client to
carry out the particular work concerned personally. This is not an easy
test to apply. Each case depends on its own particular facts. Other tests
must also be met for IR35 to apply but they are easier to apply in
There is some case law on the subject but because each case depends on its
own facts, the case law is of limited assistance.
As to how a right of a worker to substitute someone else to do any of the
work for the client is relevant to deciding whether IR35 applies to a case,
please read our Guidance Note (which you can see here).